The postal services of many countries around the world permit and/or require the printing of evidence of postage payment, such as a postal indicium, that includes a two-dimensional barcode. For example, the United States Postal Service has implemented a program known as the Information Based Indicia Program (IBIP) which permits a user to generate a postage indicium for sending a mailpiece (e.g., letter, package, etc.) that includes a human readable portion and a machine readable portion in the form of a two-dimensional barcode, such as without limitation, what is commonly referred to as a Data Matrix symbol. Such an indicium is commonly referred to as a Digital Postage Mark (DPM). In addition to encoding the value of the postage represented by such an indicium, the two-dimensional barcode often encodes other pieces of information concerning the mailpiece and/or the indicium, such as the date on which the indicium was printed, data concerning a characteristic and/or unique identifier of the printer used to print the indicium, an identifier of the sender and/or intended recipient, data concerning the location of the sender and/or intended recipient, an identifier that is assigned and is unique to each mailpiece, the weight of the mailpiece, and/or data concerning the size of the mailpiece.
Because the two-dimensional barcodes included in DPMs represent monetary value, and are thus a type of currency, it is tempting to fraudsters to copy a valid indicium having such a barcode and reuse it on other mailpieces. Even if a system of detection of duplicates is in place at the postal facilities (such as a system recording the barcodes going through and matching them against a database of all previously recorded barcodes), a number of ways of avoiding detection are possible. For example, the fraudster could send the illegitimate copy of the barcode first and the legitimate barcode afterward, making prosecution practically impossible. Alternatively, the fraudster could send all copies of the barcode at the same time from different locations so that the copies would be processed before the database is updated. Thus, it is desirable to protect such a postal indicium against copying.
One known way to protect an image, such as a postal indicium, against copying is to incorporate a watermark therein. A highly desirable form of watermark is an image-dependent dynamic watermark. Such a watermark is image-dependent in that the location at which the watermark is embedded into the image is dependent upon a characteristic of that image. Such a watermark is dynamic in that the content of the watermark, itself, is dependent upon data that is expected to change frequently, and perhaps as frequently as each time the watermark is embedded into an image. Unfortunately, considerable processing capability is needed either to process an image to determine where to embed a watermark therein to achieve image dependence, or to derive a new dynamic watermark each time the content of the watermark, itself, changes.
It is known to employ the processing capabilities built into a printer used to print postal indicia on mailpieces to incorporate a watermark into each printing of a postal indicium onto a mailpiece. However, the processing and data storage capabilities typically built into such a printer are usually limited by a need to produce such a printer at a minimal cost. As a result, it has become common practice to employ an image-independent fixed watermark in postal indicia generated within and printed by such printers. Such a watermark is image-independent in that the location at which the watermark is embedded into all images remains fixed, regardless of how an image changes or what image is used (e.g., always positioned around the center of any image, or always at given locations relative to a given corner of any image). Such a watermark is fixed in that the content of the watermark, itself, does not change such that the identical watermark is used, repeatedly. Although such a watermark accommodates the limited processing and data storage capabilities of typical printers used to print postal indicia, such a watermark more readily allows the indicia into which it is incorporated to simply be copied or scanned one time, and then recreated many times. Furthermore, improvements made in photocopying, printing and scanning equipment over time has made it easier to commit fraud by copying and reusing postal indicia, including watermarked postal indicia. Therefore, it would be desirable to be able to apply dynamic watermark information to printed images that are dependent upon the images without the necessity of significant processing power or memory in the printer device.